KSeF (Poland's mandatory national e-invoicing system) became compulsory on 1 February 2026 for the largest VAT taxpayers and on 1 April 2026 for all remaining active VAT payers. If your company has a Polish entity, a Polish branch or Polish VAT registration, invoicing software stopped being a back-office preference and became infrastructure.
The complication for foreign-owned companies is that vendor websites all claim the same three things: KSeF compliant, one-click submission, full integration. The differences only surface when KSeF rejects an invoice at 23:40 on the last day of the month, or when your external bookkeeper needs access to five entities but must not touch invoice numbering.
Here are eight questions worth asking before you commit. Each one tests a mechanism rather than a marketing claim.
1. Does it issue in the FA(3) schema, and who keeps the schema current?
FA(3) is the binding logical structure for structured invoices from 1 February 2026. Flat-rate farmer invoices (faktura VAT RR) use a separate schema, so if you purchase agricultural produce, ask about FA_RR explicitly rather than about "all invoice types".
More important than the claim itself is the process behind it. When the Ministry of Finance publishes a new schema version, does the vendor update the mapping server-side, or do you install a new release? Is there logic that picks the schema version based on the issue date, given that correction documents often reference invoices issued before the change?
A useful control question: how many days did it take you to ship FA(3) support after the documentation was published?
2. How does the software authenticate to KSeF?
This is the most technical question on the list and also the most practical. The available methods are a KSeF certificate, a qualified electronic signature, a qualified electronic seal, and a token.
The Ministry of Finance treats certificates and tokens as functionally different rather than interchangeable: a token carries the permissions granted at the moment it is generated, while a certificate serves only as a means of authentication. Permissions are then granted separately, for the tax identifier recorded on the certificate. In practice that means changing someone's scope of access does not require re-issuing their login credential.
The legal status of tokens beyond 2026 was still under consultation in mid-2026, so treat any hard cut-off date as provisional. The safer position is to pick a tool that supports certificates today, whatever the legislation settles on.
Ask about type 2 certificates as well. They are required for marking invoices in the special modes, which leads to question three.
3. What does the software do when KSeF is down?
This is where most tools fall away. Outages are not hypothetical, and the rules define several distinct modes: offline24, system unavailability, and emergency mode. Each carries its own deadline for delivering the invoice into KSeF.
An invoice issued in offline24 must reach the system by the next business day at the latest. In emergency mode the clock runs in business days from the end of the declared failure and allows 7 business days. Those are not the same numbers, and software that collapses them into a single "72 hours" counter will show you the wrong deadline.
Concrete demo questions:
Does the system detect the unavailability signal itself, or do I switch modes manually?
Does it generate the QR codes required on an invoice issued offline?
Can I see a countdown for documents still pending submission?
4. Does it pull purchase invoices, or only push sales invoices?
Half the market solves outbound only. But once the obligation applies, supplier invoices stop arriving by email as well. They sit in KSeF, and someone has to retrieve them on a regular basis.
If the software does not do this, a manual process grows next to it: somebody logs into the government taxpayer application every few days and moves documents by hand. That is the most common source of missing costs and late VAT deduction, and it is exactly the kind of process a foreign parent company will not see until year-end.
Ask about three things: automatic background retrieval, manual import for a chosen date range, and flagging of documents that need review before they are booked.
5. What do you see when KSeF rejects an invoice?
KSeF returns errors as codes and technical messages. The difference between good and bad tooling is whether you see the raw API response or a sentence telling you what to fix.
A real example: an advance invoice still in draft has no assigned number, so a settlement invoice referencing it will be rejected. The API message will not explain that. A well-designed interface says: issue the advance invoice first.
Ask to see the rejected-submission screen during the demo. If the vendor only shows the happy path, that is an answer in itself.
6. How many entities and users can it handle without permission chaos?
Critical for accounting firms and for any group running more than one Polish entity.
Check whether switching between companies happens inside one panel or through separate accounts and separate logins. Then check the permission model. The minimum is role separation: owner, administrator, accountant, view-only user. What you actually need is the ability to build a custom role, because an external bookkeeper usually should issue and submit invoices without managing the team, the KSeF connection or the numbering scheme.
In Biurko, permissions are broken down to individual operations: submitting to KSeF, cancelling a transmission, and changing the number of an issued invoice are three separate rights.
7. Can you get your data back when you leave?
Ask this before signing, not a year in. Invoices are tax documentation and you need access to them regardless of whether you are still paying a subscription.
Check for export of invoices, contractors and products to CSV or XLSX, access to PDF files, access to UPO (the official confirmation of receipt issued by KSeF), and a purchase register in a format your accountant can actually use. Ask how long data is retained after a subscription ends.
A tool with no export button is not cheaper. It is just harder to leave.
8. What exactly is included in the price?
Pricing pages rarely answer the questions that determine the invoice: whether the limit applies to documents, users or companies in the panel. Whether a second entity means a second subscription. Whether batch submission sits in the base plan. Whether purchase invoice retrieval is an add-on.
Biurko offers a FREE plan with no time limit, with paid tiers starting at PLN 19 net per month for SOLO, PLN 49 for TEAM and PLN 149 for SCALE, with a 20 percent discount on annual billing.
And one question worth putting to every vendor: what happens to my invoices if I stop paying?
Pre-decision checklist
The vendor confirms FA(3) and can describe its own schema update process.
The software supports KSeF certificates, not tokens alone.
Offline24, unavailability and emergency modes are handled as distinct deadlines.
Purchase invoices are retrieved automatically, not manually.
KSeF errors are translated into language that tells you what to fix.
Multiple entities in one panel, with permissions at operation level.
Data and UPO export available without contacting support.
Pricing answers the questions about entity, user and document limits.
Conclusion
KSeF software is a multi-year choice, because migrating mid tax year is expensive. The eight questions above take about twenty minutes in a demo and save the conversations nobody wants to have in April.
Biurko was built as a KSeF-focused tool rather than a module bolted onto an accounting suite: certificate authentication, FA(3) and FA_RR, single and batch submission, purchase invoice import, a multi-entity panel with roles, and readable error messages. The interface is available in Polish, English and Ukrainian, which matters when the operations team and the parent company do not share a language.
Create a free Biurko account and run this checklist against your own data. The FREE plan has no time limit and no card required.
FAQ
Do foreign companies with a Polish entity have to use KSeF? If the entity issues invoices subject to Polish VAT invoicing rules, yes. The obligation follows the Polish entity, not the location of the parent company. Group ERP systems typically need either a certified integration or a dedicated KSeF tool alongside them.
Can I use my existing ERP instead of dedicated KSeF software? Often yes, if your ERP vendor ships FA(3) support and certificate authentication for the Polish entity. Many international ERPs deliver this late or as a paid localisation module, which is why companies frequently run a specialised KSeF tool in parallel.
What is the difference between a KSeF certificate and a token? A token embeds the permissions granted when it is created. A certificate is purely an authentication credential, with permissions assigned separately to the tax identifier recorded on it. Certificates are issued by the Ministry of Finance certification centre and are valid for up to two years.
Is free KSeF software good enough for a small company? For a handful of invoices a month, often yes. The government provides free tools, and several commercial vendors offer permanent free tiers. You start paying when you need automation: purchase retrieval, multiple entities, offline modes and readable errors.
When is the best time to switch invoicing software? At an accounting period boundary, preserving numbering continuity. Export invoices, contractors and UPO from the old system first, then configure and test the new one against the KSeF test environment before issuing your first production document.